Why is it a noxious weed?

It is a weedy plant that is capable of establishing in a wide range of habitats. In Washington it has shown the ability to spread from a small 10 acre site to several hundred acres. It is capable of impacting agricultural and range lands.

How would I identify it?

General Description: It is a perennial herb, sometimes woody at the base, reaching 3 to 4 feet tall. It has a thick, black taproot that can extend downward for two feet. The name refers to the flowers, which open late in the day and whither early the next morning.

Flower Description: Flowers are about 3/8 in diameter and are in clusters of 3 to 5 growing from a short, hairy flowerstalk at the tips of the plant. A whorl of bracts is found at the base of each flower. The flowers have 5 reddish to lavender sepals and no petals.

Leaf Description: Leaves are oppositely arranged, heart-shaped to egg-shaped and 2-4 inches long and 1-3 inches wide. The lower to middle leaves are attached by a petiole (leaf stem). Upper leaves may be sessile (no leaf stem). Leaves are waxy and usually hairless.

Stem Description: The plant’s overall shape is bushy and the stems are oppositely branched (pairs of branches along the stem). The upper stems and leaves are sometimes glaucous (covered with a whitish or bluish waxy covering).

How does it reproduce?

It reproduces by seed and by fragmented root pieces. Seed is set from July to September. The involucre aids in the dispersal of the seeds, acting as a small umbrella which catches on vehicles.

Where does it grow?

Wild four o'clock is found in a range of habitats in eastern Washington, including orchards, alfalfa fields, rangeland, right-of-ways and disturbed areas. It can also grow along riverbeds, and in sandy, rocky, and heavily cultivated soils. Please click here to see a county level distribution map of wild four o'clock in Washington.

How do I control it?

General Control Strategy

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Mechanical Control

Hand pulling is not recommended because the stems break at the crown. The roots are strongly branched, and broken root pieces will produce sprouting. Small infestations can be spaded or dug up. Repeated mowing or cultivation will prevent seed production and lower the seed bank. Eventually the plant will die from loss of nutrient reserves stored in the root. Plow infested meadows and plant a cultivated crop for 2 years. Hoe out remaining plants.